A high intake¹ of polyunsaturated fat in the diet, while good for the heart, may lead to inflammatory bowel² disease, say researchers.

研究人员称，饮食中多不饱和脂肪的大量摄入有利于心脏，但却可能导致肠道疾病。

Some margarines contain linoleic acid

Experts believe a high intake of linoleic acid（亚油酸）, found in foods like "healthy" margarines（人造黄油）, may be implicated³ in（牵连） a third of ulcerative colitis（溃疡性结肠炎） cases.

The researchers base their findings, due to be published in Gut⁴, on food diaries from more than 200,000 people.

If the link proves to be causal, some people might want to modify their diet.

The researchers also found that a diet rich in another type of fat, omega 3 fatty acid found in oily fish such as salmon⁵（鲑，大马哈鱼） and herring（青鱼）, reduced the likelihood of developing ulcerative colitis by 77%.

Linoleic acid is a naturally occurring essential fatty acid, present in a variety of foods, including the oils of seeds and nuts, such as sunflower, safflower（红花）, soya（大豆）, corn seeds or walnut⁶（胡桃） oils.

The multinational⁷ team working on the EPIC⁸ (European Prospective⁹ Investigation¹⁰ into Cancer and Nutrition) study say there is a plausible¹¹ biological mechanism¹² that could explain why linoleic acid is linked with this bowel condition.

Cell membranes¹³

Once in the body, linoleic acid is converted to arachidonic acid（花生四烯酸）, which is a component¹⁴ of the cell membranes in the bowel.

Arachidonic acid can then be converted into various inflammatory chemicals, high levels of which have been found in the bowel tissue of patients with ulcerative colitis.

In all, 126 of the people in the study developed ulcerative colitis after an average period of four years.

After adjusting for other factors likely to influence the results, including smoking, age, total energy intake, and use of aspirin¹⁵, those whose diets included the most linoleic acid were more than twice times as likely to develop the condition as those whose diets contained the least.

Lead researcher Dr Andrew Hart of the University of East Anglia, Norwich, said: "There are no dietary modifications¹⁶ of benefit in patients with ulcerative colitis, although, based on this study's findings, a diet low in linoleic acid may merit investigation."

In the UK, people consume on average about 10g per day of linoleic acid, found in around nine level teaspoons¹⁷ of polyunsaturated margarine or three teaspoons of sunflower oil.

In the study, the people who consumed the most linoleic acid had a daily intake three times this or more.

Biologically plausible

Dr Anton Emmanual, medical director of the digestive disorders¹⁸ charity Core, stressed that the study did not prove that linoleic acid caused bowel disorders, and warned that dietary diaries could be unreliable.

However, he said: "Nevertheless there is good biological plausibility¹⁹（似有道理） of why linoleic acid can cause inflamation, and certainly Western diets are often excessive in this kind of fat.

"The omega 3 fish oils counteract²⁰ the harmful effects of lineloic acid it would be helpful to see whether diets high in fish oils reduce colitis.

"Lineloic acid may have small part to play in some patients, but factors such as smoking, bacteria and stress are likely to be at least as important."

Professor Jon Rhodes, of the British Society of Gastroenterology, said the study was interesting, but also stressed it did not prove cause and effect - further tightly controlled studies would be needed to do that.

Dr Elisabeth Weichselbaum, of the British Nutrition Foundation, said the study was interesting.

But added: "The results need to be interpreted（解释，演出） with caution.

"People who have very high intakes²¹ of omega-6 fats are likely to have a generally different diet from those with low intakes. Therefore, it may as well be possible that there are other factors that could have an effect."